Pneumatic impact hammer



Nov. 25, 1969 EIMATSU KoToNE 3,480,090

' V '4 PNEUMATIC IMPACT HAMMER Filed March 22, 1968 3 Sheets-Sheet 1 14 /3 rLos huw of am Nov. 25, 1969V EIMATSU KoToNE 3,480,090

PNEUMATIC IMPACT HAMMER 3 Sheets-Sheet 2 Filed March 22. 1968 /C/- 3 am Nov. 25, 1969 EIMATSU KoToNE 3,480,090

PNEUMATIC IMPACT HAMMER Filed March 22, 1968 3 Sheets-Sheet 5 #WEA/rola, /M/lrsu Karo/VE United States Patent() 3,480,090 PNEUMATIC IMPACT HAMMER Eimatsu Kotone, 4, Aza-Nishiyama 193, Kobayashi, Takarazuka-shi, Hyogo-ken, Japan Filed Mar. 22, 1968, Ser. No. 715,269 Int. Cl. E21c 3/04; F011 25/04, 25/02 U.S. Cl. 173-135 10 Claims ABSTRACT F THE DISCLOSURE An automatic impact hammer driven by compressed air and having la time delay chamber efective to cause the pneumatic control system to refrain from driving the opv erating piston until the pressure Within said chamber is increased to a given or predetermined value. This desired time lag is from the end of impact or power stroke to the beginning of return stroke of the piston during which compressed air is accumulated in the reservoir for the next cycle of the hammer. Also, a safety valve is provided in the pneumatic control system to prevent the piston from no-load stroking, and a closed chamber is formed between the cylinder and the tool to provide an air cushion upon return of the tool to the start position.

The present invention relates to an automatic hammer, and more particularly, to a pneumatic impact hammer which when suitably connected to a pressurized air power source is effective to automatically drive a piston against a tool and thereby give repeated impact blows to the 0bject being Worked on.

It is well-known practice in this art to utilize pneumatic hammers of this type to perform such operations as crushing concrete aggregates in construction work and driving piles into the ground at construction sites. Due to the use of tougher concrete and larger piles in modern day construction methods, the hammers to perform this work must be more powerful and have a larger mass, which in the past meant that a larger capacity air compressor as a pneumatic power source for the hammer was required. Of course, the required larger capacity of the air compressor is undesirable in that it sharply increases the overall purchase cost of the pneumatic impact harnmer accompanied with a suitable air compressor to drive the same. In the past, attempts to minimize the required capacity of the air compressor for the larger work loads without decreasing the impact power have resulted in sacrice, more or less, of necessities for safe and reliable operation of the hammer. For example, such desirable features as (l) restriction of the piston following each impact stroke to prevent reactive bouncing on the tool, (2) prevention of the piston from stroking in the case of no load being in contact with the tool, (3) protection of the cylinder and the tool from destructive shock in reaction of the impact on the return stroke of the tool, and (4) operation of the hammer from remote control, have in the past been sacriced in attempts to gain the necessary impact power with small air compressors.

Thus, one object of the present invention is to provide a pneumatic impact hammer which exerts powerful impact strokes while utilizing an air compressor of comparatively small capacity as the power source.

A more specific object of the invention is to provide a control system for a hammer of the type described wherein a desired time lag for the return stroke of piston is provided, which in turn, allows the construction of a pneumatic impact hammer that delivers maximum impact force for a given capacity of air compressor used as a power source.

A further object of the invention is to lprovide an apparatus to prevent the operating piston of pneumatic imice pact hammer from reactive bouncing on the tool following each impact stroke.

A further important object of the invention is to provide a pneumatic impact hammer with a means to prevent the operating piston from performing a work stroke when there is no object or load in contact with the tool.

Yet a further object of the invention is to provide a pneumatic impact hammer with means to absorb the impact shock between the cylinder and the tool on the return stroke of the tool.

A further object of the invention is to provide a pneumatic impact hammer with a tool holder by which the hammer is adaptable to be engageable with other machines for remote control without any significant increase in the size and weight.

Other objects and various features of the invention will be more apparent from the following description of a preferred form of the invention, which is shown by way of example only in the accompanying drawings, in which:

FIG. 1 is a front view, in vertical cross section, of a pneumatic impact hammer particularly adapted for crushing concrete aggregates and constructed in accordance with the present invention.

FIG. 2 is another front View, of the impact hammer in FIG. 1, partially in vertical cross section.

FIG. 3 is an enlarged view illustrating the lower end of the cylinder and the upper end of the tool holder of the hammer shown in FIG. 1.

' FIG. 4 is a schematic diagram of the pneumatic system and circuit of the impact hamm-er shown in FIG. 1.

The preferred embodiment of the hammer illustrated in the drawings for the purpose of disclosing the invention consists of a power cylinder 6, a drive piston 55 within said cylinder 6, a tool holder 35 attached to the lower end of said cylinder 6, and an operating tool 36, such as a chisel. To control the actuation of the drive piston 55 with the required reciprocation motion to drive the tool v36, there is provided, as best illustrated in the FIG. 4, :an upper control valve 3, a manifold 60, a lower control valve 10, a start valve 27, a change-over valve 21, an actuating Valve 13, a time delay chamber 14, and a safety valve 42, =all of which will be further dened and described in the following disclosure in this order. An air reservoir 65 shown in dotted line outline in FIG. 4 represents a source of pressurized air, such as a conventional air compressor.

The cylinder 6 comprises a wall 6 which defines an internal bore 50 or cylinder wall, an upper port 7 and a lower control port 11 extending radially through the wall 6 to alternately supply and discharge air to the cylinder 6. A cylinder head 24 seals the upper end of the cylinder 6 to form a drive chamber 51, and an annular shoulder 30 formed integrally around the wall 6' near the lower end 31 of cylinder 6 cooperates with the tool holder 34 to seal the lower end to form a return chamber 52. A small hole 53 extends radially through the wall `6 at a lower portion thereof for a purpose which will subsequently be explained. The cylinder head 24 is provided with a lever 22 supported for oscillating movement by a fulcrum or pivot pin 22'. A relay bar 25 is supported in slidable relation through a central aperture in said cylinder head 24; the upper end of said bar 25 being adapted Ato come into contact with one arm of the lever 22 to provide a driving relationship, while the lower end of said bar 25 extends into said chamber 51 so as to be adapted to be operatively contacted by the piston 55 when in the return position (opposite to that shown in the drawings). The annular shoulder 30 has an outer peripheral ilange 29 which cooperates with the upper end of said tool holder 35 to form the required air tight seal and an axially extending aperture is formed in said shoulder 30 for a purpose which will later be explained.

From the above, it will be understood that the piston 55 is Iguided along the cylinder wall 50 in the usual manner and is elfective to always divide the space of bore 50 into the drive chamber 51 which opens at the upper control port 7, and the return chamber 52, which opens at the lower control port 11. As illustrated, the lower end of the piston 55 is tapered with the end face being adapted to come into contact with the tool 36, while the upper end face of the piston 55 is adapted to come into contact with the bar 25, as previously described.

The tool holder 34 is cylindrical and coaxial with said cylinder 6, but has a larger diameter since it is coupled with the cylinder 6 at the flange 29 as mentioned above.v Accordingly, the cylinder 6 has a substantially smaller diameter than the tool holder 34. The tool holder 34 itself comprises a cylinder wall 32, an axial opening 38 at the lower end thereof to guide the reduced lower portion of the tool 36, and a plurality of radially extending apertures 33 (only one shown) opening around the wall 32 for respiration of air. Each aperture 33 is provided with a strainer 39, preferably fabricated of porous sintered alloy metal to reliably filter the incoming air; said strainer being positioned in fixed relation by the intermediary of an annular washer 37 and any number of screws 38'.

When in operation, the tool 36 is, of course, supported and guided within the tool holder 34 in slidable fashion; the lower portion extending through the opening 38 so as to come into contact with the object to be operated on. The head of the tool is, on the other hand, in the central portion thereof so as to come into operative driving contact with the piston 55. A crown 35 is formed at the periphery of the tool 36 which is to be received in a clearance 40 between the lower end 31 of the cylinder wall 6' and the upper portion of the wall 32 when the tool is in the return position, as shown. As the tool 36 approaches the return position, due to the air tight seal around the crown 35, there is always some amount of air staying within the clearance 40 between the shoulder 30 of the cylinder 6 and said crown 35, as can best be seen in FIG. 3, so that a cushion is formed, as will more fully appear below.

The upper control valve 3, which is mounted over the upper control port 7 on the cylinder wall 6', comprises a valve casing 1, a reciprocal valve member 3' in the casing 1, a spring 205, held captive at the upper end of said valve member 3' to constantly urge it downwardly, a bore 113 opening axially in the bottom of said casing 1, two bores 111 and 112 opening radially on opposite sides of the valve casing member 3', and an exhaust port 2 (see FIG. 4) in the side of the casing 1. The bore 112 is located to coincide with the upper port 7 of cylinder `6, and the bore 111 is located opposite to the bore 112 to provide an air passage between them when the valve member 3 is in the position shown. The port 2 is located just under the bore 111 and is opposite to the bore 112 to provide an air passage therewith through a narrow reduced portion adjacent the bottom of the valve member 3' when the same is in the opposite position. The valve member 3' is normally in the lowered position shown by virtue of the compression action of spring 205 plus the action of gravity, thereby opening the air passage between the bores 111 and 112 while closing the air passage between the bore 112 and port 2, as shown in FIG. 4.

The manifold 60 which is physically mounted adjacent the upper control valve 3 on the cylinder wall 6 in the embodiment shown, is provided with an inlet 4 and seven outlets 611, 612, 613, 614, 615, 616, 617. The inlet 4 is provided with an internal bushing 4 to be connected to the air reservoir 65 for pressurized air supply. The outlet 614 is connected directly to bore 111 of upper control valve 3, while the other outlets are connected to other valves by way of connections as described later.

The lower control Valve 10, which is mounted over the lower port 11 on the cylinder wall 6', comprises a valve casing 8, a valve member 10' slidably enclosed in the casing 8, a spring 210 provided in engagement with the lower end of the valve member 10 to bias it upwardly, a bore 803 opening axially in the top of casing 8, two additional bores 801 and 802 opening radially in the side of casing 8, and a discharge port 9 opening radially in the side of casing 8. The bore 802 is located to meet the lower port 11 of cylinder 6 and the bore 801 is located opposite to the bore 802 to provide an air passage between them, when the valve member 10' is in the position opposite to that shown in FIG. 4. The port 9 is located just under the bore 801 and also opposite to the bore 802 to provide an air passage between them as shown in FIG. 4. The valve member 10' is normally in the raised position by virtue of the compression action of spring 210, thereby opening the air passage between the bore 802 and discharge port 9 while closing the air passage between the bores 801 and 802, as shown in this ligure.

The start valve 27, which is physically lmounted over the small hole 53 on the cylinder wall 6 comprises a valve casing 26, a valve member 27' slidably enclosed in the casing 26, a spring 227 provided on the outer end of valve member 27 to bias the same inwardly, a valve stem 28' lixedly extending from the inner end of valve member 27', a central aperture 54 opening axially in the inner end of casing 26 to slidably guide the valve stem 28', and a closure ball 28 affixed to the free end of valve stem 28'. A bore 264 opens axially in the inner end of casing 26, and three bores 261, 262, 263 open radially in the side of casing 26 to control the passage of air through the valve 27. The central aperture 54 is located to meet the hole 53 of cylinder 6 (see FIG. l), thereby permitting the ball 28 to come into and out of the cylinder bore 50 through the said hole 53 and to engage the piston 55. The bore 261 is located opposite the bore 262 to provide an air passage between them, while the bore 263 is located adjacent the axial bore 264 also to provide an air passage between them. The valve member 27' integral with the stem 28 and ball 28 is normally in the inward position by the action of the spring 227, thereby closing the air passage between the bores 261 and 262 as well as the passage between the bores 263 and 264 while having the ball 28 project into the cylinder bore 50 below the tapered end portion of the piston 55.

The change-over valve 21 which is mounted above the start valve 27 on the cylinder wall 6' (see FIG. l) comprises a valve casing 19, a valve member 21 slidably enclosed in the casing 19, a spring 221 provided on the lower end of valve member 21 to bias it upwardly, an integral valve rod 23 extending from the upper end of valve member 21', a central aperture 23' opening axially in the top of casing 19 to slidably guide said valve rod 23 through, thirteen bores 901, 902 913 opening radially in the side of casing 1'9 to control the passage of air through said valve 21 and four discharge ports 201, 202, 203, 204, opening radially in the side of casing 19. The upper end of valve rod 23 engages the outer arm of the lever 22, it being remembered that the inner arm comes into contact with the bar 25. The bores 902 and 908 are located opposite to each other with port 203 being positioned in the same plane between the two so as to provide an air passage to the port 203 from each of said bores 902, 908. The bores 901 and 907 are likewise located opposite to each other to provide an air passage between them when aligned with the reduced portion of the valve member 21' as shown. Similarly located opposite to each other for communication via the adjacent reduced portion are the bores 903 and '909, the bore 910 and port 201, the bores 904 and 911, the bore 912 and port 202, the bores 905 and 913, the bore 906 and port 204. The valve member 21 integral with the rod 23 is normally in the raised position through the action of spring 221, thereby opening the air passages between the bores 901 and '907, between the bores 903 and 909, between the bores 904 and 911 and between the bores 905 and 913 while closing the air passages between the bore 912 and port 203, between the bore 908 and port 203, between the bore 910 and port 201, between the bore 912 and port 202, between the bore 906 and port 204, as shown in FIG. 4.

The actuating valve 13 which, as particularly shown in FIG. 2, is physically mounted between the manifold 60 and the change-over valve 21 on the cylinder wall 6' and as shown in FIG. 4 comprises a valve casing 12, a valve member 13 slideably enclosed in the casing 12, a spring 213 provided on the upper end of valve member 13 to bias it downwardly, a valve rod 16 extending integrally from the lower end of valve member 13', a central aperture 16 opening axially in the bottom of casing 12 to slidably guide the valve rod 16, a bore 126 opening in the bottom of casing 12, and ve bores 121, 122, 123, 124, 125 opening radially in the side of casing 12, all to control the passage of air through the valve 13. The bores 121 and 122 are located opposite to the bores 123 and 124, respectively, each respective pair to provide an air passage between them while the bore 125 is located adjacent the axial bore 126, also to provide an air passage between these two. The valve member 13' integral with the rod 16 is normally in the lowered position, as illustrated, by the action of the spring 213 plus its own weight,

thereby closing the air passage between the bores 121 and 123, between the bores 122 and 124, between the bores 125 and 126.

The time delay or time lag chamber 14, which has a fixed volumetric capa-city, is mounted ibeneath the actuating valve 13. The time lag chamber 14 is provided with an upper aperture 171 (note FIG. 2), opening axially in the top, a lower aperture 172 opening axially in the bottom, and a `bore 173 opening radially in the side. EX- tending in blocking relationship to the upper aperture 171 is a head 15 which is slidably and air-tightly supported in a mating bore 15' in the casing 12. The head 15 is in engagement with the rod 16 of actuating valve 13 so that the latter is raised against the elasticity of spring 213 of actuating valve 13 when the air pressure is increased over a given value Within the chamber 14; the head 15 being adapted to be returned to the lowered position by the action of said spring 213 and the total weight of head 15 plus valve member 13 and rod 16 when said pressure is decreased under the given value. The lower aperture 172 is equipped with a conventional regulating valve 1S (see FIG. 18) to regulate the ow of pressurized air into the chamber 14 at a desired rate which is determined in accordance with the supply capacity of the air compressor used and the required impact of the hammer. The head 15 of said valve 13 is normally in the lowered position as shown through the action of the spring 213 and the total weight of itself plus valve member 13 and rod 16.

The safety valve 42 which is physically mounted on the shoulder of cylinder wall 6 comprises a valve casing 41; a valve member 42 enclosed in the casing 41 in slidable relation, a spring 242 provided on the upper end of valve member 42 to urge it downwardly, an integral valve stem 43 extending from the lower end of said valve member 42', and a central aperture 43 opening axially in the bottom of the casing 41 to slidably guide the said valve stern 43. Further, a pair of bores 411 and 412 are provided opening radially in the side of said casing 41 oppositely to each other to provide an air passage between them when the reduced portion of the valve member 42 is aligned therewith, as in FIG. 4. The valve stem 43 slidably projects through the aperture 30' into the clearance 40 between the lower portion of cylinder wall 6 and the upper portion of tool holder wall 32, and is engageable with the crown of the tool 36. The valve member 42 is normally in the lowered position through the action of spring 242 plus its own weight, thereby closing the air passage between the bores 411 and 412. That is, this condition is in effect when the valve stem 43 projects substantially into the clearance due to the crown 35 being lowered suciently to disengage from the valve stem 43.

The pneumatic circuit or control system of the invention is best illustrated in FIG. 4. The manifold 60 is connected to the valves 3, 10, 27, 21, 13 by way of supply .lines D, F, A, B and G, C and E, respectively, while the valves 3, 10, 27, 21, 13, 42 and the time delay chamber 14 are all interconnected by way of control air lines a1, a2 a3: b1 b21 Cl C2a el: e2 g1: g2' The Supply lines and the control lines are contemplated as Vbeing in any form of conventional piping or conduits, or can be in any other form of direct connections, such as machined passageways in the housings of the various components. In FIG. 4, the cylinder 6 and piston 55 as well as the air reservoir 65 are shown in dash-dot lines for a clear understanding of the operation of the circuit, as will presently be explained.

Prior to the operation of the pneumatic impact hammer, the piston is initially in the position shown in FIG. 1, that is, down in contact with the tool 36, which in turn is in a return or raised position with the lower or operative end in contact with the object to be operated on, or in the present specific example, the object to be crushed, such as concrete aggregate. In this state of operation, the crown 35 of the tool 36 is in suicient engagement with the stem 43 of safety valve 42 to have the valve member 42 raised against the force of the spring 242, thereby opening the air passage between the bores 411 and 412, as shown in FIG. 4. Meanwhile, the presence of the piston 55 pushes the ball 28 of start valve 27 fully into the hole 53 in the cylinder wall 6 against the action of spring 227, which it will be remembered constantly urges the valve member 27' to be shifted outwardly, therefore opening the air passage between the bores 261 and 262 as well as the air passage between the bores 263 and 264, also as shown in FIG. 4.

Now, assuming a supply of compressed air is delivered to the manifold from the air reservoir 65 through the inlet 4', compressed air is supplied from said manifold 60 to the time delay chamber 14 by way of a combined air passage made up of the outlet 611 of manifold 60, supply line A, bores 261 and 262 of the start valve 27, line al, bores 411 and 412 of the safety valve 42, line a2, and regulating valve 18. Since the control line a3 from the chamber 14 is closed at the bore 902 in the normal raised position of the member 21 of the change-over valve 21, the air supplied via the path just described increases pressure within the chamber 14, which is of xed capacity, in proportion to the flow rate regulated by the valve 18. After a period of time, the pressure within the chamber 14 has been raised to a predetermined value sucient to raise the head 15 of the activating valve 13 and through the valve rod 16 raise the valve member 13 against the action of the spring 213. Meanwhile, compressed air is also supplied from the manifold 60 to the start valve 27 by way of another combined air passage made up of the outlet 617 of manifold 60, supply line G, bores 913 and 905 of changeover valve 21, control line g1, and bore 263 of valve 27. Since the line g2 is closed at the bore 906 of the valve 21 in the normal raised position of the valve member 21, the air supplied through said bore 263 tends to keep the valve member 27 of the start valve 27 in the outward position against the elastic action of the spring 227 even after the piston 55 moves out of biasing contact with the ball 28 of said valve member 27.

As stated, when the pressure gets to the predetermined value in the time delay chamber 14, the head 15 begins to be raised so as to drive the valve member 13 upwardly. This movement is gradual with the specific rate depending upon the elasticity of spring 13 which is in engaging relation with the valve member 13. This initially small, slow rise of valve member 13 eventually causes the opening of the air passage between the bores and 126. Compressed air is thus supplied from the manifold 60 to the valve 13 by way of an air passage made up of the outlet 612 of manifold 60, supply B, bores 907 and 901 of change-over valve 21, control line b1, and bore 125 of valve `13, and thence, to the control line b2. Since the line b2 is closed at the bore 908 at this time, the air supplied through the bore 125 has an additive elect to the upward driving force against head 15, thereby quickly raising the valve member 13 to its final position and opening the air passage between the bores 122 and 124, as well as the air passage between the bores 121 and 123.

In the fully raised position of the member 13' of the actuating valve 13, compressed air is supplied on one hand from the manifold 60 to the upper control valve 3 by way of combined air passage made up of the outlet 613 of manifold 60, supply line C, bores 122 and 124 of the valve 13, control line c1, bores 904 and 911 of the changeover valve 21, line c2, and bore 113 of said upper control valve 3; while air is supplied on the other hand from the manifold 60 to the lower control valve 10 by way of another combined air passage made up of the outlet 615 of the manifold 60, supply line E, bores 121 and 123 of the valve 13, control line e1 bores 903 and 909 of the valve 21, control line e2 and bore 803 of said valve 10. The air supplied through the bore 113 raises the valve member 3 against the action of the spring 205, thereby closing the air passage between the bores 111 and 113, the latter of which communicates with the upper section 51 of this cylinder 6 (FIGS. 1 and 4), but opening the air passage between said bore 112 and the exhaust port 2. Thus, any pressure initially present in the upper section 51 of cylinder bore `50 is vented to the atmosphere by way of a combined air passage made up of the upper port 7 of cylinder 6, bore 112 and port 2 of the valve 3, or in other words, through this air passage pressure is reduced to atmospheric in the upper section 51.

Meanwhile, the pressurized air supplied through the bore 803 lowers the valve element 10 against the biasing action of the spring 208, thereby closing the air passage between the bore 802 and the exhaust port 9, but opening the air passage between the bores 802 and 801. As a result, compressed air is supplied from the manifold 60 to the lower section 52 of the cylinder bore 50 (FIGS. 1 and 4) by way of a combined air passage made up of the outlet 616 of the manifold 60, supply line F, bores 801 and 802 of the valve 10, and the lower port 11 of cylinder 6 (see FIG. 1). As a result of the pressure differential existing between the sections 51 and 52 of cylinder bore 50, the piston 55 is at this point lifted upwardly for the initiation of return stroke of said piston 55.

As the piston 55 proceeds on its return stroke, it goes out of contact with the ball 28, thereby conditioning the start valve 27 to be closed by inward movement of member 27' due to the force of the spring 222 as soon as the pressure on the end face of said member 27' through the bore 263 is relieved. Thus, at this time, compressed air continues to flow into the time delay chamber 14 by way of the air passage through the bores 261 and 262 of the start valve 27, thereby continuing to slowly drive the head 15 and the valve member 13 upwardly against the elasticity of spring 213.

The rising operating piston 55 finally comes up into contact with the bar 25 at a location below the cylinder head 24, and, as explained above, this causes the rotation of the lever 22 on the fulcrum 22 in a counterclockwise directed as viewed in FIG. 4 to in turn lower the valve member 21 of the change-over valve 21 against the action or force of the spring 221. In the thus assumed lowered position of the change-over valve 21, the four air passages are closed between the bores 901 and 907, between the bores 903 and 909, between the bores 904 and 911, between the bores 905 and 913, while the tive air passages are opened between the bore 902 and exhaust port 203, between the bore 908 and the same exhaust port 203, between the bore `910 and the exhaust port 201, between the bore 912 and the exhaust port 202, and between the bore 906 and the exhaust port 204.

At this point in the cycle, air is no longer supplied to the start valve 27 through the bore 263 but said valve is exhausted through the latter to the atmosphere by way of the combined air passage `made up of the bore 264 of the valve 27, control line g2, the bore 906 and the port 204 of the valve 21, thereby permitting the valve member 27 to return to the inward position through the biasing force of the spring 227 g the ball 28 projecting out of the hole 53 into the cylinder bore 50 due to the raised mode of the piston 55. Accordingly, compressed air is no longer supplied to the time delay chamber 14 by way of the air passage through the bores 261 and 262 of valve 27 but discharged out of it into the atmosphere by way of an air passage made up of the bore 173 of chamber 14, control line a3, bore 902 and exhaust port 203 of valve 21. In addition, compressed air is no longer supplied to the actuating valve 13 through the bore 125 but discharged out of it into atmosphere by 'way of an air passage made up of the bore 126 of valve 13, line b2, bore 908 and exhaust port 203 of valve 21. Now that the pressure is released from the valve 13 and the chamber 14 through the bore 126 and the bore 173 respectively, the valve member 13 with the rod 16 is returned to the original lowered position together with the head 15 by the force of the spring 213 plus weights of the elements. Accordingly, compressed air is no longer supplied to the upper control valve 3 through the bore 113, but is discharged out of the valve 3 into the atmosphere by way of an air passage made up of the bore 113 of valve 3, line c2, bore 912 and exhaust port 202 of the valve 21, thereby permitting the valve member 3 to return to the original lowered position by the action of spring 205 plus the weight of the valve member 3. Also, compressed air is no longer supplied to the lower control valve 10 through the bore 803 but is discharged out of the valve 10 into the atmosphere by way of an air passage made up of the bore 803 of the Valve 10, line e2, bore 910 and port 201 of the valve 21, thereby permitting the valve member 10' to return to the original raised position by the action of spring 210.

On one hand, in the raised position of lower control valve 10, the pressure is released from the lower section 52 of cylinder bore 50 into the atmosphere by lway of an air passage made up of the lower port 11 of cylinder 6 (FIG. 1), bore 802 and port 9 of valve 10. In other words, pressure is reduced to `atmospheric in the lower section 52 of the cylinder 6. On the other hand, in the lowered position of upper control valve 3, compressed air is supplied from the manifold 60 to the upper section 51 of cylinder bore by way of an air passage made up of the outlet 614 of manifold 60, bores 111 and 112 of the valve 3, and upper port 7 of cylinder 6 (see FIG. l). As a result of the pressure differential now existing between the sections 51 and 52 of cylinder bore 50, the piston 55 is naturally driven downward on the power stroke during which it is being accelerated not only by the pressure differential but also by its own weight which is substantial in the type of device described herein. At a midpoint of the power stroke the piston 55 reopens the start valve 27 in readiness for the next cycle and at the bottom of the stroke the piston 55 gives a powerful impact to the tool 36 which in turn is effective to crush the object being worked on (not shown). The weight of the hammer against the tool 36 immediately after the power stroke returns the tool 36 to the raised position so that the piston 55 is then in the original position as shown in FIG. 1. The change-over valve 21 is also returned to the original raised position by the force of spring 221 after the piston 55 is removed from operative contact with the bar 25.

Assuming that a constant supply of compressed air is delivered to the manifold 60, it should now be understood that the impact hammer continuously repeats the abovedescribed automatic operation to effectively crush the object being worked on as long as said object remains in contact with the tool 36.

Since it takes a certain time period to increase the pressure within the chamber 14to the predetermined value suiicient to raise the head 15 against the biasing force of the spring 213, there is a corresponding time lag or delay for each return stroke of the piston 55, i.e. a delay from the end of each impact stroke to the beginning of the successive return stroke. Advantageously, during this time lag, compressed air is not consumed by the hammer but accumulated in the air reservoir 65 connected to the air compressor. The longer the time lag prior to initiation of the return stroke of piston S, the higher the pressure that is capable of being built up in the air reservoir 65 so that it can be seen that the supply capacity of the air compressor used can be considerably less than would otherwise be required. Furthermore, it follows that the longer the time lag, the more powerful the impacts that can be exerted with an air compressor of a given capacity. According to an important feature of the invention, the desired time lag for the return stroke of piston 55 is easily determined by adjusting the flow rate of compressed air through the regulating valve 18 which in turn means that the air hammer can be adjusted for optimum operation in relation to the supply capacity of air compressor and the required impact force of the hammer. It has been found as a practical matter, that With a moderate time lag for the return stroke of the piston 55, the impact hammer of the invention exerts substantially more powerful impacts than has heretofore been obtainable with an air compressor of comparable capacity.

Moreover, both the upper control valve 3 and the lower control valve remain in their normal positions (IFIG. 4) during the above-described time lag, and therefore, the operating pressure is maintained in the upper section 51 of the cylinder bore 50` while atmospheric pressure is maintained in the lower section 52, respectively."This feature assures the retention of the piston 55 in close operative contact with the tool 36, thus eliminating undesirable reactive bouncing following each impact stroke.

When the hammer is not in position to be operated, that is, when there is no object or load in contact with it, the tool 36 is not returned to the upper position by the weight of the hammer, so that the crown 35 remains disengaged from the stem 43 of safety valve 42. The disengaged crown 35 thus leaves the valve member 42 with stem 43 of the safety valve 42 in the lowered position so that the compressed air supply from manifold 60 to chamber 14 is interrupted by closing of the air passage between the bores 411 and 412. This means that the piston 55 is prevented from beginning the return stroke and remains in `contact with the chisel 36 so that there is no chance of accidental initiation of the power stroke. In other words, the piston 55 can not begin a power stroke with no object or load being in contact with the tool 36.

Since there is always some amount of air trapped between the shoulder 30 of cylinder 6 and the crown 35 of tool 36, the tool 36 is prevented by a cushion of the air from direct collision with the cylinder 6 upon return to the upper position of FIG. l. In other words, the clearance 40 acts to prevent destructive shock and resultant damage to the cylinder 6 and the tool 36 of the hammer that might otherwise occur as a result of the rapid return of the tool 36 to its upper or return position in response to the reaction force caused by the impact of the power stroke.

For remote control or operation of the impact hammer of the present invention from a shovel loader, power shovel, bulldozer or other similar machines, a suitable means is preferably provided on the wall 32 of tool holder 34 to engage with the supporting structure of such machines. In certain cases, this may require such modifications as increase in the thickness of tool holder Wall 32, but it should be understood that no substantive changes need to be made with respect to the novel features of the hammer as disclosed and claimed herein. In particular, no changes having to do with the cylinder 6 and any other operating part of impact hammer need to be made to so support the hammer for remote control Clearly, modications of such features as the thickness of cylinder wall 6 are not required so that any significant increase in the size and weight of hammer as a whole is avoided with the present design.

It is contemplated that the combination time lag chamber 14 of fixed capacity and the regulating valve 18 could be replaced with a chamber of variable capacity for similar regulation of the time lag for the return stroke of piston 55 without departing from the broader aspects of the present invention. Also, the tool 36 which in the embodiment disclosed would take the form of a chisel or the like to crush solid material, such as concrete aggregate, could be replaced with a driving head to engage with a pile for driving piles in construction sites, if desired.

It will thus be seen from the above that the pneumatic impact hammer constructed in accordance with the present inventtion is capable of exerting more powerful impacts than heretofore possible even when driven by an air compressor of comparatively small capacity. Furthermore, this is accomplished without sacrificing recognized necessities for reliable and safe operation of the hammer.

While a preferred embodiment of the invention has been illustrated by way of example in the drawings and particularly described, it will be understood that modications may be made in the shown embodiment without departing from the invention. Moreover, the features of the embodiment shown in the drawings are deemed to be mutually interchangable so `far as they are compatible.

I claim:

1. An automatic hammer to be driven by a source of compressed air to give repeated cycles of operation to impart a series of impacts to an object comprising a cylinder having upper and lower ends and being provided with an upper port and a lower port, a tool holder axially secured to the lower end of said cylinder, a tool slidably supported in said tool holder for reciprocating movement, a piston mounted for reciprocating movement within said cylinder and positioned for operative driving engagement with said tool, a first valve means to supply and discharge compressed air through said upper port of said cylinder to respectively second valve means to supply and discharge compressed air through said lower port of said cylinder to respectively increase and decrease pressure under said piston, a third valve means to actuate said rst and second valve means so as to supply said pressure at one of Said ports while discharging pressure from the other, delay means to provide a desired time lag to the actuation of said third valve means in response to the completion of the previous cycle of operation, means to control said delay means to vary time lag, and means to change-over said third valve means to switch said first and second valve means and said delay means, whereby said piston is automatically reciprocated on alternate impact and return strokes during each cycle by the pressure differential across said piston with a time lag being provided from the end of each impact stroke to the beginning of the successive return stroke.

2. An automatic hammer according to claim 1, wherein said third valve means includes an operating means responsive to said delay means and a plurality of air passages to be opened and closed in response to said delay means, said air passages being connected to both of said rst and second valve means by said change-over means, whereby both of said rst and second valve means are pneumatically actuated by said change-over means to discharge compressed air through said upper port to decrease pressure over said piston and to supply compressed air through said lower port to increase pressure under said piston and thereby driving said piston upwardly on a return stroke after said time lag following each cycle.

3. An automatic hammer according to claim 2, wherein said third valve means is further provided with an auxiliary operating means to facilitate the opening and closing of said plurality of air passages in response to said delay means.

4. An automatic hammer according to claim 2, wherein said delay means comprises a chamber of fixed capacity and an adjustable means to regulate the rate of ow of said compressed air into Said chamber, said chamber being provided with a movable actuating head slidably supported therein, an inlet to supply said air to said chamber to increase pressure therein to operate said head, an outlet to discharge air from said chamber to release said head, said movable head being engaged in a driving relationship with said operating means of Said third valve means so as to open said plurality of air passages to ac tuate simultaneously both of said first and second valve means in response to the pressure in said chamber being raised above a predetermined value whereby said time lag is provide, and means operative during said time lag to maintain said rst and second valve means in position to maintain the pressure over said piston higher than under same.

5. An automatic hammer according to claim 2, wherein said delay means comprises a chamber of variable capacity provided with a movable head therein, an inlet to supply said air to said chamber to increase pressure within said chamber, and an outlet to discharge said air to decrease pressure within said chamber, said movable head being engaged in a driving relationship with said operating means of said third valve means so as to open said plurality of air passages to actuate simultaneously both of o said iirst and second valve means in response to the pressure being raised over a given value Within said chamber, whereby a desired time lag is provided for raising pressure up to said given value within said chamber by varying the capacity of said chamber.

6. An automatic hammer according to claim 4, wherein is further provided start valve means to control the supply of air to said delay means, said start valve means having feeler means at the lower portion of said cylinder to come into contact with said piston at the end of each impact stroke, whereby the pneumatic supply to said time lag means is initiated at the end of each impact stroke of said piston.

7. An automatic hammer according to claim 6, wherein said change-over valve means is provided with a plurality of air passages, trip means positioned at the upper portion of said cylinder to come into contact with said piston at the end of said return stroke, said air passages respectively connected to both of said iirst and second valve means, said third valve means, said delay chamber, and said start valve means, whereby, while said trip means is out of contact with said piston, said air passages permit said third valve means to condition said rst and second valve means to drive said piston on said return stroke, to condition said delay chamber to prevent decreasing pressure in said valves, and to condition said start valve means to supply compressed air to said time delay chamber and whereby after said trip means is contacted by said piston, said air passages permit said third valve means to condition said rst and second valve means to drive said piston on said impact stroke by releasing said operating means and by exhausting said time lag chamber to decrease pressure therein to allow release of said head, and said start valve means is conditioned to stop supplying said compressed air to said delay chamber.

S. An automatic hammer according to claim 1, wherein said cylinder is provided with an annular shoulder extending from the outer wall near the lower end thereof, said annular shoulder being provided with a flange at the periphery thereof, said tool holder having an inner diameter larger than the outer diameter of said cylinder and secured axially to said cylinder at said shoulder in airtight relation to provide an annular clearance therebetween one end of which is closed at said shoulder, said tool being provided with a crown at the upper periphery, said crown being adapted to be inserted into said annular clearance in slidable and air-tight relation with both the inner wall of said tool holder and the outer wall of said cylinder so as to trap a suicient amount of air to form a cushion to absorb shock caused by the return of said tool toward said cylinder in reaction of the impact given to the object during the impact stroke.

9. An automatic hammer according to claim 8, wherein is further provided a safety valve means comprising a sensing means and an air passage to be opened and closed in response to said sensing means, said air passage being positioned between said delay means and said start valve means, said sensing means slidably extending downwrd through said shoulder for engagement with said crown of said tool only when said tool is in the upper position, whereby said delay means and said start valve means are interconnected with each other only when said tool is in the upper position indicating contact with an object, thereby preventing said piston from being actuated when there is no object in contact with said tool.

10. An automatic hammer according to claim 8, wherein said tool holder is adapted to engage with other machines for remote control therefrom.

References Cited UNITED STATES PATENTS 2,296,647 9/1942 McCormick 91-306 2,341,463 2/1944 Maytham 91-306 2,944,530 7/1960 Severinsen 91-305 3,133,472 5/1964 Zollinger 173-135 JAMES A. LEPPINK, Primary Examiner Us. C1. XR. 

